Detent plunger assembly and control method

A detent plunger assembly (48) for selectively controlling movement of a manually operated shift lever (42) in a controller-assisted, manually shifted vehicular transmission system (10), said shift lever movable in a predetermined shift pattern to move a shift member (70) from a neutral position to at least one engaged position for engaging a selected gear ratio, said system including a system controller for receiving input signals indicative of system operating conditions and processing same according to logic rules to issue command output signals to system actuators, including a detent plunger actuator (108), said plunger assembly comprising:

• a detent plunger (82) movable in a first direction to inhibit movement of said shift member and in a second, opposite direction for not inhibiting movement of said shift member;
• a differential area piston (86) associated with said plunger for imparting movement thereto, said piston having a first piston surface (104) defining a first chamber (106) and a second piston surface (100) defining a second chamber (102), said first piston surface having an area greater than the area of said second piston surface, pressurization of said first chamber urging said plunger to move in said first direction and pressurization of said second chamber urging said plunger to move in said second direction;
• a first conduit (106A) connecting said first chamber to a a selected one of common source of pressurized fluid (S) and an exhaust (EXH), a second conduit (102A) constantly connecting said second chamber to said common source of pressurized fluid;
• and
• a spring (110) biasing said plunger in said first direction, said spring applying a force less than the force of pressurized fluid from said common source acting on said second piston surface.